Anode for cathodic protection



May 8, 1962 R. A. CHEVIGNY ET ANODE FOR CATHODIC PROTECTION i ||'+a 3| l II Filed July 51, 1959 lll TITANIUM ALLOY INVENTORS Raymoncl llcheu'iqny yHenTi Richaud H nay United States Patent Filed July 31, 1959, Ser. N0. 830,784 Claims priority, application France g- 1953 2 Claims. (Cl. 204-196) This invention relates to an anode for cathodic protection and more particularly to a sacrificial anode for use in protecting iron objects immersed in sea water and the like.

When objects such as ships are immersed for long periods of time in salt water they are subjected to considerable corrosion due to electrolytic action. For that reason it is usual to use a so-called cathodic protection, wherein a sacrificial anode is used having a lower electrolytic potential than the material of which the object to be protected is made. Sometimes this protection is brought about by the formation of a galvanic action be tween the metal to be protected and the sacrificial anode; sometimes a direct current is connected between the auxiliary anode and the metal to be protected. In the past anodes made of steel, graphite, or platinum have been used, although most of these materials have drawbacks. For instance, steel anodes are rapidly destroyed. Those which are formed of graphite show a tendency to become very brittle, while platinum anodes are very expensive. At times the metal titanium has been proposed for use in the anode, but it suffers from the nature of a strong polarization so that the auxiliary source of electrical current must be of rather high voltage. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the present invention to provide a novel anode for cathodic protection and more particularly for the cathodic protection of metals using an auxiliary source of electrical current.

Another object of this invention is the provision of an anode which has a fairly long life, which does not become brittle, and which is relatively inexpensive to manufacture.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawing setting forth in detail an illustrative embodiment of the invention, this being indicative, however, of but one of the various ways in which the principle of the invention may be employed.

In said annexed drawing:

The single figure is a schematic illustration of the method in which the anode of the invention may be applied to the protection of an iron ship.

Referring now to the drawing, the anode of the invention, indicated generally by the referencenumeral 10,

is shown in use as associated with an iron or steel ship 11 intended for use in a body 12 of sea water. As is evident in the drawing, the anode is separated electrically from the ship 11 by electrical insulation 13. A source 14 of direct electrical current is connected between the anode 10 and the ship 11, the positive poles of the source being connected to the anodes and the negative pole being connected to the ship.

The ship 11 is made of iron and, as is well known, would readily be attacked by the salt water if no means were provided for protecting it. The anode 10 consists of an alloy containing a predominant proportion of titanium; the alloy is characterized as a composition of matter that contains 3,033,775 Patented May 8, 1962 at least one element which lowers the polarization voltage of titanium. For instance, titanium alloys will be used which contain one or more members such as cobalt, nickel, manganese, zinc, tin, or the like which have the effect of lowering the polarization potential of titanium. Such an alloy may also contain aluminum. It is particularly advantageous to use a titanium alloy in which the additional element amounts to .5 to 10% by weight of the elements. It should be noted that the anode 10 is used without a coating of any sort, contrary to the usual practice of using pure titanium which has been platinum plated. Furthermore, the alloy of the anode 10 may have its polarization potential further lowered by a heat treatment such as annealing or quenching followed by a tempermg.

An example of the use of an anode made according to the invention is as follows:

An iron plate was placed in sea water at room temperature with an anode formed of an alloy of titanium having 4% aluminum and 4% manganese. The anode was connected to the positive pole of a generator of direct current electricity and the iron sheet was connected to the negative pole. The test was carried on for 500 hours with a cathodic current of 150 milliamperes per square meter. The voltage after two hours (approximately at the beginning of the test) was three volts. The voltage after 100 hours was 2.8 volts and the voltage after 500 hours was 3 volts. There was negligible loss of weight of the titanium electrode and there was a negligible loss of weight for the iron plate. The iron sheet showed no trace of corrosion after the test.

A second example of the use of the anode of the invention involved the comparison of an iron plate having an anode formed of pure titanium with a similar iron plate having an anode having titanium alloy with 4% manganese both being tested in sea Water. In the first case, when the pure titanium anode was used with an anodic current density of 0.2 amp. per sq. decimeter (20 amps. per sq. meter), a voltage of at least 8.5 volts was necessary. In the test with the titanium alloy having a 4% content of manganese, it was only necessary to use 4.5 volts to maintain the same current. When the current density was decreased to 0.0015 amp. per sq. decimeter (0.15 amp. per sq. meter) the pure titanium anode required a voltage of 6.5 volts while the alloy anode required only 3 volts to maintain that current.

Other modes of practicing the principle of the invention may be employed, changes being made as regards the details described, provided the features stated in the following claim, or equivalent of such, be employed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent is as follows:

1. Apparatus for the cathodic protection of an iron device immersed in salt water, comprising an anode, a source of direct current electricity connected to the device at its negative terminal and to the anode at its posi tive terminal, the anode consisting of an alloy of titanium and a metal selected from the class consisting of manganese, cobalt, nickel, zinc, and tin, the proportion of the total of the said metals being from 0.5% to 10% by weight, the total titanium being substantially or over by weight.

2. Apparatus as recited in claim 1 wherein the said alloy includes aluminum.

References Cited in the file of this patent UNITED STATES PATENTS 2,636,856 Suggs et al Apr. 28, 1953 2,822,269 Long Feb. 4, 1958' 2,878,173 Obermann Mar. 17,1959 

1. APPARATUS FOR THE CATHODIC PROTECTION OF AN IRON DEVICE IMMERSED IN SALT WATER, COMPRISING AN ANODE, A SOURCE OF DIRECT CURRENT ELECTRICITY CONNECTED TO THE DEVICE AT ITS NEGATIVEE TERMINAL AND TO THE ANODE AT ITS POSITIVE TERMINAL, THE ANODE CONSISTING OF AN ALLOY OF TITANIUM AND A METAL SELECTEED FROM THE CLASS CONSISTING OF MANGANESE, COBALT, NICKEL, ZINC, AND TIN, THE PROPORTION OF THE TOTAL OF THE SAID METALS BEING FROM 0.5% TO 100% BY 